Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.
OPSWAT - OPSWAT offers an advanced threat detection and prevention platform.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
HackerOne - HackerOne provides a platform designed to streamline vulnerability coordination and bug bounty program by enlisting hackers.
Better Uptime - We call you when your website goes down
Forcepoint Web Security Suite - Internet Security